1. Field of the Disclosure
The present invention relates to a process for the preparation of a composition comprising propylene glycol from glycerol. In particular, the present invention relates to a hydrogenolysis process wherein glycerol is reacted with a transition metal catalyst at elevated pressures and temperatures in the presence of hydrogen and an alkanol containing 1 to 8 carbon atoms and a water solubilized alkali metal base, where the amount of water is preferably held to a minimum.
2. Brief Description of Related Technology
Propylene glycol, known also by the systematic name propane-1,2-diol, is an organic compound (a diol alcohol), usually a tasteless, odorless, and colorless clear oily liquid that is hygroscopic and miscible with water, acetone, and chloroform. Industrially, propylene glycol is most commonly produced by propylene oxide hydration. Different manufacturers use non-catalytic high-temperature process at 200-220° C. or catalytic route which proceeds at 150-180° C. in presence of ion exchange resin or small amounts of sulfuric acid or alkali. Typically, final products contain 20% 1,2-propanediol, 1.5% of dipropylene glycol and small amount of other polypropylene glycol. Pure propylene glycol can be obtained after rectification.
Industrial uses of propylene glycol include but are not limited to, moisturizers to maintain moisture in medicines, cosmetics, food, tobacco products, as a flavoring agent in Angostura and Orange bitters, as a solvent for food colors and flavorings, as a humectant food additive, labeled as E number E1520, as a carrier in fragrance oils, as a food grade antifreeze, in smoke machines to make artificial smoke for use in firefighters training and theatrical productions, in hand sanitizers, antibacterial lotions, and saline solutions, as a main ingredient in many cosmetic products, including baby wipes, bubble baths, and shampoos, as the primary ingredient in the “Paint” inside a Paintball, as a base ingredient in aircraft deicing fluid and some automobile antifreezes, and in cryonics.
U.S. Pat. No. 6,403,844 issued to Zhang et al. describes a process for condensed phase catalytic hydrogenation of lactic acid to propylene glycol. Particularly, it provides for a process for production of propylene glycol with high yield and selectivity in an aqueous reaction mixture of lactic acid and hydrogen with an essentially pure elemental ruthenium catalyst on an inert support at elevated pressure and temperature. Further still, it provides for a process wherein the catalyst is a ruthenium salt deposited on a microporous support, reduced to ruthenium on the support with hydrogen, and oxidized in the presence of oxygen to provide a ruthenium oxide surface on the surface of the ruthenium metal and wherein the catalyst is maintained in the surface oxidized state until it is reduced with hydrogen prior to the reaction process.
Glycerol is a chemical compound with the formula HOCH2CH(OH)CH2OH. This colorless, odorless, viscous liquid is widely used in pharmaceutical formulations. Also commonly called glycerin or glycerine, it is a sugar alcohol, and is sweet-tasting and of low toxicity. It is a central component of lipids.
Until recently, synthetic glycerol was mainly manufactured at an industrial scale from epichlorohydrin. Since glycerol forms the backbone of triglycerides, it is produced on saponification or transesterification. Soap-making and biodiesel production are respective examples. Glycerol is a 10% by-product of biodiesel production (via the transesterification of vegetable oils). This has led to a glut of crude glycerol in the market, making the epichlorohydrin process no longer economical. A great deal of research is being conducted to try to make value-added molecules from crude glycerol (typically containing 20% water and residual esterification catalyst) obtained from biodiesel production, as an alternative to disposal by incineration.
Accordingly, there exists a need for alternative propylene glycol production particularly from glycerol.